Simultaneous isomerization of pentane and hexane with selective fractionation



Apnl 28, 1964 G. F. AssELlN 3,131,235

SIMULTANEOUS ISOMERIZATION 0F' PENTANE AND HEXANE WITH SELECTIVE FRACTIONATION Filed Nov. 23, 1960 A 7' TURA/EVS.

United States Patent fce ,131,235 Patented Apr. 28, 1964 SIMULTANEOUS ISOMERIZATION F PEN- TANE AND EEXANE WITH SELECTIVE FRACTONATIN George F. Asselin, Mount Prospect, Ill., assigner to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Filed Nov. 23, 1960, Ser. No. 71,278 6 Claims. (Cl. Mtl-683.68)

The present application is a continuation-impart of my copending application Serial No. 698,991, led November 26, 1957, now abandoned. The present invention relates to the isomerization of saturated hydrocarbons in the presence of hydrogen and an isomerization catalyst. More specifically, the present `invention is directed toward a combination process involving selective fractionation and the simultaneous isomerization of pentane and hexane. The unique combination of the particular series of process steps, encompassed by the present invention, results in three individual product streams, each of which possesses a higher octane blending value than the original fresh hydrocarbon charge to the process.

The relatively recent introduction, within the automotive industry, of internal combustion engines having a high compression motor fuels possessing unusually high anti-knock characteristics. Motor fuels possessing high octane blending values, an indication of the anti-knock characteristics i thereof, are required for the purpose of utilizing the maximum horsepower output of the internal combustion engine. In turn, the demand for higher and higher octane motor fuels has resulted in the need for steadily increasing quantities of these high-quality hydrocarbons. The group of iso-parainic hydrocarbons, containing from about tive to about six carbon atoms per molecule, is one particular source of hydrocarbons possessing unusually high octane blending values. The object of the present invention is to provide a series of particular processing steps for the simultaneous isomerization of pentanes and hexanes, resulting in significantly increased volumetric yields of isoparainic hydrocarbons, with respect to the yields heretofore obtained.

Therefore, in a broad embodiment, the present invention relates to a process for effecting the isomerization of a hydrocarbon charge containing hydrocarbons having from about ve to about six carbon atoms per molecule, which process comprises removing isopentane from said hydrocarbon charge, reacting the resulting deisopentanized hydrocarbon charge in a reaction zone containing an isomerization catalyst and maintained under isomerization conditions, separating the reaction zone efliuent into a hydrogen-rich gaseous phase and a liquid phase, separating the latter into a first hydrocarbon fraction containing pentanes, and a second hydrocarbon fraction containing hexanes, combining said petane containing fraction with the hydrocarbon charge prior to removing isopentane therefrom, removing at least a portion of said second fraction from said process and isohexanes hom the remainder, and combining the deisohexanized portion with the aforesaid deisopentanized charge prior to reacting the same in said reaction zone.

Another embodiment of the present invention involves a process for isomerizing an isomerizable hydrocarbon charge containing hydrocarbons having from about ve to about six carbon atoms per molecule, which process comprises combining said charge with a pentane-containing isomerized product, removing isopentanes from the resulting mixture and passing the deisopentanized portion of said mixture, along with hydrogen, into a reaction zone maintained under isomerization conditions and having disposed therein a catalytic composite of aluratio has necessitated the utilization of mina, combined halogen and a platinurn-group metallic component, separating the resulting reaction zone etliuent to provide a hydrogen-rich gaseous phase and a liquid phase containing isopentane and isohexane, separating said liquid phase into a iirst hydrocarbon fraction containing pentanes and a second hydrocarbon fraction containing hexanes, recycling said pentane-containing fraction to combine with said hydrocarbon charge prior to the removal of isopentane therefrom, withdrawing at least a portion of said second fraction from said process, removing isohexanes from the remainder of said second fraction, and combining the deisohexanized portion of said second fraction with the aforesaid deisopentanized charge and hydrogen prior to reacting the same in said reaction zone.

A more limited embodiment of the present invention is directed toward a process for isomerizing an isomerizable hydrocarbon charge containing hydrocarbons having from about five to about six carbon atoms per molecule, which process comprises combining said charge with a pentanerich isomerized product, removing isopentane from the resulting mixture and passing the deisopentanized portion of said mixture, along with hydrogen, into a reaction zone maintained at a temperature within the range of from about 200 F. to about 800 F., and under a pressure of from about to about 2000 pounds per square in'ch, and having disposed therein a catalytic composite of alumina, platinum and from about 2.5% to about 5.0% by weight uorine, calculated as the element, separating the resulting reaction zone effluent to provide a hydrogen-rich gaseous phase and a liquid phase containing isopentane and isohexane, separating said liquid phase .into a first hydrocarbon fraction containing pentanes and a second hydrocarbon fraction containing hexanes, recycling said pentane-containing fraction to combine with said hydrocarbon charge prior to the removal of isopentane therefrom, withdrawing atleast a portion of said second fraction from said process, removing isohexanes from the remainder and combining the deisohexanized portion of said second fraction with the aforesaid deisopentanized charge and hydrogen prior to reacting the same in said reaction zone.

From the foregoing embodiments, it is seen that the process of the present invention involves the particular steps of selective fractionation and simultaneous isomerization of a hydrocarbon mixture containing pentanes and hexanes. A typical hydrocarbon mixture, to be utilized as charge to the present process, contains isopentane, normal pentane, 2,2-dimethylbutane, 2,3-dimethylbutane, Z-methylpentane, 3-methylpentane, normal hexane, methyl cyclopentane, and cyclohexane, etc. In accordance with the present invention, a hydrocarbon charge, of the foregoing composition, is admixed with a previously isomerized product consisting essentially of isopentane and normal pentane. This mixture is introduced into a first fractionation zone serving as a deisopentanizer, from which an isopentane-rich stream is withdrawn as an overhead product, the deisopentanized portion of the remainder of the mixture being admixed with a hexane-containing stream derived from an isomerized product by fractionation, land hydrogen, this mixture being passed into an isomerization reaction zone. The total reaction zone eiiiuent, rich in isoparainic hydrocarbons having from about five to about six carbon atoms per molecule, is passed into a suitable separation zone from which a hydrogen-rich gaseous phase is removed and recycled to combine with the mixture of deisopentanized charge, and hexane-containing isomerized product. The normally liquid hydrocabons are passed into a fractionation zone serving as a C5-C6 splitter, from which a pentane-rich overhead fraction is removed and recycled to combine with the fresh charge prior to passing the latter into the deisopentanizer. The heavier C6 hydrocarbons are removed as a bottoms fraction from the molecule. particular processing steps include high over-all yields junits higher than produced C5-C6'splitter, and passed into a fractionation zone serv- `ing as a'deisohexanizer, from which an overhead product of isohexanes is removed. An essential feature of the present invention is the withdrawal of at least a portion of the C-Cs splitter bottoms fraction'from the process,

to prevent'the accumulation of cyclic hydrocarbons in the charge to the isomerization reaction zone. As hereinafter indicated, another essential feature of the present invention is the point at which the cyclic hydrocarbons, as a drag-stream, are Withdrawn from the process. According tothe process of the present invention, the drag-stream is a Y por-tion of the bottoms fraction from the C5-C6 splitter Yindividual product streams, all of which possess octane blending values substantially in excess of the octane rating of the original hydrocarbon charge stock, and the total volumetric yield of which is as highas about 94.0%, based upon the quantity of hydrocarbonsinitially charged to the process. The low octanerating components of the original .hydrocarbon charge stock are converted into highoctane products through the combination isomerization and selec- Vtive fractionation-process` as -hereinabove set forth. The

Y process of the present invention selectively separates the low-octane components, and independently converts them Y tohighfoctane components. `By separating the W octane components, the charge tothe isomerization reaction zone consists primarily of normal paraflnic hydrocarbons .having from about live to about six carbon atoms per The numerous advantages of the foregoing of high-octane products, mild operation of the isomerization reactionV zone,l inherently yresulting in an extended catalyst life, and conversion of the low octane rating normal paratlinic hydrocarbons in the absence of the high octane ratingisomers. In addition, the foregoing processing procedur ein which the original hydrocarbon charge is initially subjected to fractionation to remove isopentane, Y andthe liquid reactor efHuent is segregated into a pentanecontaining fraction and ahexane-containing fraction, affords lesser over-all fractionation duty: fractionation duty refers to the size ofthe various vfractionators, the quantity of heating required to effect proper, acceptable fractiona- Y tion therein. In addition tothe economic considerations involved in fractionation duty, the process of the prent invention affords the very substantial. advantage of producing a total CG-parailinic hydrocarbon product which possesses an octane rating (F-l with 3.0 cc.` TEL/ gal.) 3.4 from conventional processes in which the `total reaction zone effluent is first deisopentanized, or.-Where the initial hydrocarbon charge is first introduced into a CB-CS hydrocarbon fractionation zone together Vwith the total reaction Zonel etlluent, etc. Furthermore, the withdrawal of a drag-stream, containing cyclic hydrocarbons, from the C5-C6 splitter bottoms fraction, results in the need for a smaller fractionator, to serve las the deisohexanizer, in addition to other advantages resulting from the Withdrawal at this particular point.

The combination process of the present invention may be further understood through reference to the accompanying drawing. In the drawing, numerous valves, controls, coolers, condensers and other miscellaneous appurtenances have been eliminated as not being essential to the complete understanding of the present invention. The incorporation of these, and other modifications, may be made by one possessing sulcient skill within the art of petroleum processing, and are not considered to be outside the broad scope and spirit of the present invention as set forth in the appended claims.

A hydrocarbon charge stock, containing hydrocarbons having from -above ylive to about six carbon atoms per molecule, enters the process through line 1, being adunixed with la pentane-containing isomerized product in line 15, the mixture being introduced into deisopentanizer 2. It is understood that the pentane-containing stream in line 7.5 may be combined with the charge in line 1, or may enter deisopentanizer 2 at a point slightly above that at which the charge in line 1 is introduced, and that the flatter scheme is intended to be included within the scope of the presen-t invention. The combined hydrocarbon charge is separated in deisopentanizer 2 such that a substantially pure isopentane fraction is removed via line 3 as an overhead product. The deisopent-anized portion of the combined charge is removed from deisopen tanizer 2 via line 4, is admixed with a hexane-containing isomen'zed product in line 21 and passed into heater 5 wherein the temperature of the ihydrocarbon mixture -is raised to the desired ope-rating level. As indicated in the drawing, the combined deisopen-tanized hydrocarbon charge pass-ing into heater S is admixed with la gaseous recycle stream, rich in hydrogen, entering via line 12 from compressor lll. Although not indicated in the drawing, in some instances the recycled hydrogen-rich gaseous phase from compressor il may be passed via line 12 to combine with 4the heated hydrocarbon charge in line 6 prior to Vpassing the same into isomerization reaction zone 7.

Isomerization react-ions may be effected in isomerization reaction zone 7 at varying yconditions of tempera' ture, pressure, liquid hourly space velocity, and hydro gen to hydrocarbon mol ratio to convert the normal paratlns into isoparafns. The temperature'will'generally be dictated by the particular isomerization catalyst disposed Within isomeriza-tion reaction zone 7, and will be within thel range of from about 2001 F. to about 800 F. The pressure selected for the isomerization reaction zone 7 will be Within the range of lfrom about to about 2000 .pounds per square inch. The liquid hourly space velocity (defined as the volume of liquid charge per hour per volume of catalyst disposed Withinthe reaction zone) will range from about 0.1 to about; 10.0 or more, 'the only limitation being that nea-rly equiJ librium Ymixtures of isomerizedhydrocarbons are obtained in the reaction zone elluent. Hydrogen is utilized to minimize cracking, land to maintain the surface of the catalyst in a carbon free condition. 'Ihe quantity of hydrogen utilized will range from about 0.25 to about 10.() mols, or more of hydrogen per mol of hydrocarbon. The consumption of hydrogen will be exceedingly small, and Will be Within the range of from about 30 to about 100 standard cubic feet per barrel of total liquid hydrocarbon charge `to the reaction zone.

The catalyst disposed within reaction zone 7 may be any suitable isomerization catalyst comprising a carrier material, an acid-acting componen-t, and a hydrogenation component. rIlhe carrier material may be selected from various diverse refractory inorganic oxides, including, silica, alumina, silica-alumina, silica-alumina-magnesia, silica-alumina-Zirconia, alumina-zirconia, silica-zirconia etc. These various carrier materials will have surface areas .ranging from about 25 Vto about 500 square me ters per gram, depending upon the particular method se lected for the preparation thereof. vThe effectiveness of the carrier material, the acid-acting function may be added .thereto by incorporating therewith quantities of combined halogen. The amount of combined halogen may be varied yfrom about 0.01% to about 8.0% by weight, calculated as the element, and based upon the weight of the carrier material. Both fluorine and chlorine may be used `to supply the combined halogen, although the preferred halogen, which will be utilized with Ithe alumina-carrier material, is iiuorine in an amount of from about 2.5% to yabou-t 5.0% by Weight, calculated as the element thereof.

Following lthe formation of the alumina, the hydrogenaltion component will be combined therewith. The hydrogenation component will usually be selected from lthe group consisting of groups Vi-A and VIII of the periodic table, or mixtures thereof. Such hydrogena-tion components include chromium, molybdenum, tungsten, iron, cobalt, nickel, and the platinum group metals including platinum, palladium, ruthenium, rhodium, osmium, and

iridium. The platinum-group metals are preferred, and

of these metals, platinum is particularly preferred. The hydrogenation component of the catalytic composite disposed in reaction zone 7 will be utilized in an amount of from about 0.1% to about 10.0% by weight, calculated as ythe element, and based upon the weight of the carrier material. With the particularly preferred platinumgroup metals, the quantity utilized will range from about 0.1% to about 2.0% by weight. A particularly preferred lcatalytic composite will comprise 0.4% by weight of platinum, 4.0% by weight of fluor-ine, the remainder being alumina.

Due to equilibrium considerations, and because it is often desirable and/or advisable to effect the isomerization reactions at the lowest possible temperature, from about 200 F. to about 500 F., the catalytic composite may also be prepared by impregnating composites as `hereinabove described with a metallic halide of the Friedel- Crafts type. For example, an excellent low temperature isomerization catalyst may be prepared by impregnating aluminum chloride onto ya composite of platinum, alumina and combined halogen. The process of the present invention may be effected in the presence of other catalysts, but not necessarily with equivalent results. Such other catalysts include aluminum chloride sludge, aluminum bromide sludge, etc., which may be employed along with hydrogen chloride, hydrogen bromide, etc.

The total reaction zone eiuent is passed, after cooling, through line 8 into separator 9. A gaseous phase, rich in hydrogen, is removed via line 12 and raised to the reaction zone operating pressure by compressor 11. The

hydrogen-rich gaseous phase is recycled via line 12 to combine with the liquid hydrocarbon charge to reaction zone 7. As indicated in the drawing, the hydrogen-rich recycle gas stream is combined with the liquid hydrocarbon reaction zone charge prior to raising the latter to the desired operating temperature. However, as hereinbefore set forth, the recycled hydrogen may enter the process to combine with the previously heated hydrocarbon charge, in line 6. Although not indicated in the drawing, makeup hydrogen, to replace the relatively minor quantity consumed Within ythe process, may be introduced into line or line 12 from any suitable source. The normally liquid hydrocarbons, following the removal of the hydrog gen rich gaseous phase, are removed from separator 9 via line 13. The total liquid isomerized product is transmitted via line 13 into C5-C6 splitter 14. An overhead product, consisting essentially of pentanes, is removed via line 15, and is combined with the fresh hydrocarbon charge in line 1, prior to passing the latter into deisopentanizer 2, or, as previously stated, passed directly into deisopentanizer 2 at a point above line 1. The heavier, C5 hydrocarbons are removed from the bottom of C5-C6 splitter 14 via line 16 and introduced into deisohexanizer 19. At least a portion of the bottoms product from C5-C6 splitter 14, is removed in line 17 containing valve 18 as a drag stream from the process, prior to passing the bottoms product into deisohexanizer 19. This drag stream is necessary in order to reject the cyclic hydrocarbons entering the process with the original hydrocarbon charge, thus avoiding an intolerably high cyclic concentration in the reactor feed. Conventional, prior art processes, reject such cyclic hydrocarbons either in a small bottoms stream from deisohexanizer 19, with the recycle hexanes to the reactor being Withdrawn as a side-cut, or merely withdraw a portion of the deisohexanizer bottoms prior to introducing the same into the isomerization reaction zone. The process of the present invention, wherein the drag-stream is withdrawn from the bottoms product of the C-CG splitter, eliminates two serious disadvantages of conventional processes. The present method is much more effective in achieving the desired cyclic rejection, and further, a loss of about 8.0 octane-rating units (F-l with 3.0 icc. TEL/ gal.) will be avoided with respect to the drag stream. Thus, in accordance with the present invention, the drag stream is withdrawn from the present process from line 16 via line 17 containing valve 18. The remainder of the C5-C6 splitter bottoms is introduced into deisohexanizer 19 from which an isohexane-rich stream is removed as overhead product through line 20. The remaining portion of the C5-Cs splitter bottoms fraction is removed via line 21 and recycled to combine with the deisopentanized hydrocarbon mixture in line 4, prior to passing the same into heater 5 and isomerization reaction zone 7.

To illustrate another of the many advantages inherent in the combination process of the present invention, the fresh charge might be introduced into the pentane-hexane splitter, which arrangement unnecessarily swells the needed volume of the reactor due to the isopentane contained in the fresh feed, which must now enter the reaction zone instead of being short-circuited through the deisopentanizer directly to the iso-pentane products stream. By introducing the fresh hydrocarbon charge first into a deisopentanizing zone, and passing the total reaction zone effluent into the pentane-hexane splitter, the diiculty of splitting the effluent into the desired two fractions is lessened considerably since the feed to the splitter comprises an approximately 60/ 40 volumetric ratio of isopentane to normal pentanes, instead of an approximately equal volume of total pentanes which are nearly n-pentane, as would be the case if the fresh charge and reactor eluent were combined in a deisopentanizer. In addition, considering the C5 hydrocarbon load, the present process reduces the load on the C5-C6 splitter by about one-half.

Considering the C6 hydrocarbon performance of the process of the present invention, the hexanes contained in the fresh hydrocarbon charge pass immediately from the deisopentanizer directly to the reaction zone, without mingling with, and degrading the quality of the reactor effluent upstream of the deisohexanizer. By this method it is possible to produce a higher quality hexane-parainic product than with the conventional methods of the prior art processes, the increase in quality being about 3.4 octane units.

The following example is given to illustrate further the method of the present invention, and to indicate clearly the benefits to be afforded through the utilization thereof. It is not intended that the process of the present invention be limited unduly to the character of the charge stock, the operating conditions and/or the catalyst employed within the example.

The catalyst disposed Within the reaction zone comprises an alumina carrier material with which has been composited 4.0% by weight of combined uorine, calculated as the element. Following the formation of the alumina-combined fluorine composite, platinum is composited therewith through the use of an impregnating technique. The impregnating technique involves soaking, dipping or otherwise immersing the alumina-combined iiuorine composite in an aqueous solution of chloroamount of 1333 barrels per day, comprising 670 b./d. f.

of total pentanes, 530 b./d. of total hexanes, and 133 b./d. of cyclic hydrocarbons, is combined with 679 b./ d. of apentane-containing isomerized product. Following the removal of 637 b./d. of isopentane, having an octane v rating' of approximately 108.6 (F-l with 3.0 cc. TEL/ gal),

the remaining portion of the mixture, in an amount of about 1375 b./d. is admixed with hydrogen and about 767 b./d. of a hexane-containing isomen'zed product, the mixture being raised to a temperature of about 700 F., and thereafter passed into the reaction zone containing the aforementioned catalyst. The total reaction zone effluent is passed into a high-pressure separator, operating at approximately room temperature, from which a hydrogen-rich gas stream is recycled to combine with the deisopentanized charge and the hexane-containing isomerized product. The total reaction zone liquid eiuent, about 2059 b./d., is passed into a fractionation zone which operates to provide a light hydrocarbon fraction containing isopentane and n-pentane, and a second heavier hydrocarbon fraction containing isohexanes, normal hexane and cyclic compounds. The lighter fraction is recycled, in an amount of about 679 b./d., within the process to combine with the 1333 b./d. of fresh charge, the mixture being fractionated to remove the isopentane therefrom. The heavier fraction is passed in an amount of about 953 b./d., following the removal of 427 b./d. as a drag-stream, into the deisohexanizer from which approximately 186 b./d. of isohexanes are removed. The deisohexanized, bottoms material is then recycled, in anv amount of about 767 b./d., to combine with the deisopentanized charge and hydrogen prior to passing the Vsame into the reaction.

-The product distribution, resulting from the foregoing example of the process, is given in the following table.

,The various charge and product streams are indicated,-

and the concentration of pentanes, hexanes and cyclic hydrocarbons in each stream.

Tabulaed Data-Prduct Distribution Total Total Total Total (J6-paraf- Stream, h./d. Pentanes Hexanes Cyclies Stream tin Octane Ratingl Fresh Charge 670 530 133 1, 333 78. 4

y Reactor Charge 712 1,000 430 2, 142 80. 7

v Reactor Eluent 679 950 430 2,059 88.6

CrC splitter Isohexane 186 102. 2

Drag Stream 294 133 427 88.6

Total Produets 637 294 133 1, 250 93. 9

1Octane rating for the pal'an'ic hexane portion of the various total streams is tlhe F41 Rafting with 3.0 ce. TEL/gal.

As hereinbefore set forth, the 637 b./d. of isopentane, withdrawn as a product stream, possesses an octane rating, F-l with 3.0 cc. TEL/ gal., of about 108.6. The isohexane product stream possesses an octane rating, of 102.2; the427 b./d. of the drag stream, contains 294 b./d. of a hexane fraction having the indicated octane rating of 88:6; the 133 b./d. of cyclic hydrocarbons possesses an octane rating of about 103.0, the octane blending value of the total drag-stream being approximately 93.0, F-l with 3 .0 cc. TEL/ gal.

The total volumetric yield of the three individual product streams is 1250 b./d., or about 94.0% by volume, based upon the total fresh charge to the process. The octane rating of the total quantity of C5 parainic hydrocarbons, contained in the three individual product streams,

is indicatedas being 93.9. This .octane blending value.A

is approximately 3.4 units greater than that obtained from conventional processes which, as hereinbefore set forth, for example, combine the total reaction zone efuent with the fresh hydrocarbon charge as feed to the C5-C6 splitter, and which processes withdraw the drag stream at some other point in the process, for example, following the removal of isohexanes from the total hexane-containing fraction.

The foregoing example and specification illustrates the method of the present invention and indicates the benefits to be afforded through the utilization thereof.

I claim as my invention:

1. A process for effecting the isomerzation of a hydrocarbon charge containing hydrocarbons having from about live to about six carbon atoms per molecule, which process comprises removing isopentane from said hydrocarbon charge, reacting the resulting deisopentanized hydrocarbon charge in a reaction zone containing an isomerization catalyst and maintained under isomerization conditions, separating the reaction zone eluent into, a hydrogen-rich gaseous phase and a liquid phase, separating the latter into a first hydrocarbon fraction containing pentanes and a second hydrocarbon fraction containing hexanes, combining said pentane-containing fraction with the hydrocarbon charge prior to removing isopentane therefrom, removing a portion of said second fraction from said process, fractionating the remainder of lsaid second fraction to separate isohexanes therefrom,; and combining the deisohexanized portion of said second fraction containing normal hexane with the aforesaid deisopentanized charge prior to reacting the same in said reaction zone.

2. A process for isomerizing an isomerizable. hydrocarbon charge containing hydrocarbons having from about live to about six carbon atoms per molecule, which process comprises combining said charge with a pentanerich isomerized product, removing isopentane from. the resulting mixture and passing the deisopentanizedvwportion of said mixture with hydrogen intoa reaction` zone containing an isomerization catalytic vcomposite ofa refractory inorganic oxide and a platinum-group metal, and maintained under isomerization conditions, separatingthe resulting reaction zone etfluent to provide `a hydrogenrich gaseous phase and a liquid phase containing isopentane and isohexane, separating said liquid phase .into a first hydrocarbon fraction containing pentanes .andsa second hydrocarbon fraction containing hexanes, recycling said pentane-containing fraction to combine with said hydrocarbon charge prior to the removal of isopentane therefrom, removing a portion of said second fraction from said process, fractionating the remainder of said second fraction to separate isohexanes therefrom, and combining the deisohexanized portion of said second fraction containing normal hexane with the aforesaid deisopentanized charge and hydrogen prior to reacting the same in said reaction zone.

3. A process for isomerizing an isomerizable hydrocarbon charge containing hydrocarbons having from about tive to about six carbon atoms per molecule, which process comprises combining said charge with a pentane-rich isomerized product, removing isopentane from the resulting mixtureand passing the deisopentanized portion of said mixture, along with hydrogen, into a reaction zone maintained under isomerization conditions and having disposed therein a catalytic composite of alumina, combined halogen and a platinum-group metallic component, separating the resulting reaction zone efluent to provide a hydrogen-rich gaseous phase and a liquid phase containing isopentane and isohexane, separating said liquid phase into a first hydrocarbon fraction containing pentanes and a second hydrocarbon fraction containing. hexanes, recycling said pentane-containing fraction to combine Vwith said hydrocarbon charge prior to the removal of isopentane therefrom, withdrawing a portion of said second fraction from said process, removing isohexanes from the remainder of said second fraction, and combining lthe-deisohexanized portion of said second fraction containing normal hexane with the aforesaid deisopentanized charge and hydrogen prior to reacting the same in said reaction zone.

4. The process of claim 3 further characterized in that said catalytic composite comprises alumina, platinum and from about 0.1% to about 8.0% by Weight of combined halogen.

5. The process of claim 3 further characterized in that said combined halogen is tluorine in an amount Within the range of about 2.5% to about 5.0% by weight, calculated as the element.

6. A process for isomerizing an isomerizable hydrocarbon charge containing hydrocarbons having from about five to about six carbon atoms per molecule, which process comprises combining said charge with a pentane-rich isomerized product, removing isopentane from the resulting mixture and passing the deisopentanized portion of said mixture, along with hydrogen, into a reaction zone maintained at a temperature Within the range of hom about 200 to about 800 F. and under a pressure of from about 100 to about 2000 pounds per square inch, and having disposed therein a catalytic composite of alumina, platinum and from about 2.5% to about 5 .0% by Weight of uorine, calculated as the element, separating the resulting reaction zone euent to provide a hydrogen-rich gaseous phase and a liquid phase containing isopentane and isohexane, separating said liquid phase into a first hydrocarbon fraction containing pentanes and a second hydrocarbon fraction containing hexanes, recycling said pentane-containing fraction to combine with said hydrocarbon charge prior to the removal of isopentanes therefrom, withdrawing a portion of said second fraction from said process, removing isohexanes from the remainder of said second fraction, and combining the deisohexanized portion of second fraction containing normal hexane with the aforesaid deisopentanized charge and hydrogen prior to reacting the same in said reaction zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,834,823 Patton et a1 May 13, 1958 2,900,425 Bloch Aug. 18, 1959 2,905,619 Sutherland Sept. 22, 1959 2,908,735 Haensel Oct. 13, 1959 2,968,631 Carr et al lan. 17, 1961 OTHER REFERENCES Kellog Oil and Gas Journal, Vol. 55, No. 12, p. 155, March 25, 1957.

Pure Oil Oil and Gas Journa vol. 55, No. 12, p. 158, March 25, 1957. 

2. A PROCESS FOR ISOMERIZING AN ISOMERIZABLE HYDROCARBON CHARGE CONTAINING HYDROCARBONS HAVING FROM ABOUT FIBE TO ABOUT SIX CARBON ATOMS PER MOLECULE, WHICH PROCESS COMPRISES COMBINING SAID CHARGE WITH A PENTANERICH ISOMERIZED PRODUCT, REMOVING ISOPENTANE FROM THE RESULTING MIXTURE AND PASSING THE DEISOPENTANIZED PORTION OF SAID MIXTURE WITH HYDROGEN INTO A REACTION ZONE CONTAINING AN ISOMERIZATION CATALYTIC COMPOSITE OF A REFRACTORY INORGANIC OXIDE AND A PLATINUM-GROUP METAL, AND MAINTAINED UNDER ISOMERIZATION CONDITIONS, SEPARATING THE RESULTING REACTION ZONE EFFLUENT TO PROVIDE A HYDROGENRICH GASEOUS PHASE AND A LIQUID PHASE CONTAINING ISOPENTANE AND ISOHEXANE, SEPARATING SAID LIQUID PHASE INTO A FIRST HYDROCARBON FRACTION CONTAINING PENTANES AND A SECOND HYDROCARBON FRACTION CONTAINING HEXANES, RECYCLING SAID PENTANE-CONTAINING FRACTION TO COMBINE WITH SAID HYDROCARBON CHARGE PRIOR TO THE REMOVAL OF ISOPENTANE THEREFROM, REMOVING A PORTION OF SAID SECOND FRACTION FROM SAID PROCESS FRACTIONATING THE REMAINDER OF SAID SECOND FRACTION TO SEPARATE ISOHEXANES THEREFROM, AND COMBINING THE DEISOHEXANIZED PORTION OF SAID SECOND FRACTION CONTAINING NORMAL HEXANE WITH THE AFORESAID DEISOPENTANIZED CHARGBE AND HYDROGEN LPRIOR TO REACTING THE SAME IN SAID REACTION ZONE. 